The present invention relates to an imaging apparatus adapted to electrically implement image restoration processing.
It is known that when an object that provides a subject is formed on the imaging plane of an imaging device by way of an optical system such as a zoom lens, the image taken by the imaging device is more blurred by the influences of aberrations of the optical system than the original object: it is poorer in image quality.
The intensity distribution g of the then image is represented by g=f*h+n (*: convolution integral) (A) where noise n is added to the convolution of the luminance distribution f of the original object and the point spread function (PSF for short) that is indicative of the imaging capability of the optical system. The elements g, h and n being already known, the luminance distribution f of the original object may be figured out of Eq. (A).
The technique of deblurring the optical system by signal processing to obtain an ideal image is called the image “restoration or deconvolution”.
A typical prior art of applying such image restoration to a digital camera is known from Patent Publication 1.
Patent Publication 1 sets forth an image processing method wherein, on the basis of a signal (for an image taken by an imaging apparatus (for instance, a blurred image), a restoration filter based on a point spread function is applied to image restoration processing while care is taken of information about image deterioration at the taking time, thereby generating a less deteriorated image.
For specific restoration filters, there is the mention of a Wiener filter, a common inverse filter, or the like.
It is described that the restoration filter is generated while taking care of information about image deterioration at the taking time.
It is described that the information of which care is taken includes that analytically found out of physical factors such as taking conditions (exposure time, exposure dose, distances up to subjects, focal lengths, etc.) and performance information of the imaging apparatus (optical characteristics of lenses, identification information of the imaging apparatus, etc.) or estimated out of the outputs of measuring devices such as acceleration sensors or the like.
Such Wiener filters and common inverse filters as mentioned above are also referred to in Non-Patent Publication 1.
Other than the methods using such restoration filters, computation methods capable of implementing electrical image restoration processing using a restoration filter based on a point spread function are known as the maximum entropy method from Non-Patent Publication 2, and as the Tikhonov-Miller method, the Richardson-Lucy method, the Van Cittert method and the Landweber method from Non-Patent Publication 3.
In the digital camera field, on the other hand, preference is now being given to the small-format, slimmed-down type. Of camera size, the thickness direction has larger influences on optical system size; the arrangement of an optical system gets more important to achieve slimness.
There is also a mounting need for a high-zoom-ratio optical system arrangement having a zooming function capable of inducing large changes in the angle of view.
There is further a growing need for a small F-number, fast optical system capable of receiving a lot more light.
Patent Publication 1
    JP(A) 2000-20691Non-Patent Publication 1    “Image Processing” published by the CG-ARTS AssociationNon-Patent Publication 2    “An Introduction to Data Processing for Scientific Instrumentation and Measurement” edited and written by Satoshi Kawada under the supervision of Shigeo MinamiNon-Patent Publication 3    “Fast Deblurring Algorithms” edited by S. H. M Allon, M. G. Debertrand and B. T. H. M. Sleutjes, the Internet.
A problem with efforts to meet such needs for an optical system, however, is that the optical system tends to get bulky due to the need of making sure optical performance.
The reasons are that when there is a high-zoom-ratio arrangement provided, the imaging apparatus tends to get bulky so as to make sure the amount of movement of lens groups; when there is a small F-number arrangement provided, there are large aberrations occurring, making the PSF worse; and efforts to correct such aberrations at the optical system itself work against compactness because of the need of using a lot more lenses for correction of aberrations.
The prior arts showing such image restoration methods as mentioned above are troublesome to operators, because images taken by the imaging apparatus must once be written in recording media and then subjected to signal processing outside the imaging apparatus.
The aforesaid prior arts say nothing about the optimum arrangement of an optical system underlying such image processing, although they disclose electrical image restoration processing.